1. Field of the Invention
The present invention relates to a backlight unit having a protection circuit, and more particularly, to a backlight unit having a protection circuit that can protect lamps or an inverter in the event of lamp failure by sensing an abnormal voltage by using center-taps of secondary coils of a current balancing circuit that maintains current in each lamp balanced.
2. Description of the Related Art
Recently, as compared to existing display devices, LCD display devices that can be reduced in size and thickness have attracted attention. In particular, among the LCD display devices, an LCD TV has much attention. The LCD display device includes a backlight unit that emits light.
FIG. 1 is a configuration view illustrating a backlight unit according to the related art.
Referring to FIG. 1, a backlight unit according to the related art includes an inverter 10, a current balancing circuit 20, a lamp group 30, a sensing circuit 40, and a determination circuit 50. The inverter 10 converts DC power to AC power that is required to drive lamps. The current balancing circuit 20 includes a plurality of current balancing transformers that maintain alternating current, supplied from the AC power from the inverter 10, balanced. The lamp group 30 includes a plurality of lamps each of which receives the AC power from a secondary coil of each of the current balancing transformers of the current balancing circuit 20. The sensing circuit 40 senses voltages on the basis of the amount of current flowing into the lamps by a plurality of resistors and diodes that are individually connected to primary coils of the current balancing circuit 20. The determination 50 compares the voltage sensed by the sensing circuit 40 with a predetermined reference voltage and determines an abnormal operation in each of the lamps.
The backlight unit according to the related art includes the current balancing circuit 20 that has the current balancing transformers each of which includes the primary coil and the secondary coil having a predetermined winding ratio therebetween in order to maintain the amount of current flowing into the lamps constant. The primary coils of the above-described current balancing circuit 20 transmit the lamp driving power from the inverter 10 to corresponding lamps LAMP1 to LAMP4, respectively. The amount of current induced in the secondary coils is constantly maintained when each of the lamps of the lamp group 30 operates a normal operation. When each lamp performs an abnormal operation, that is, an open-circuit or a short-circuit occurs, the amount of current in the corresponding secondary coils increases to maintain current in each lamp balanced.
The above-described sensing circuit 40 senses a voltage on the basis of the amount of current in the secondary coil that changes according to the operation of the lamp. As described above, in order to maintain current balance, the secondary coil is electrically connected to another secondary coil of the neighboring current balancing transformer to thereby form one loop. Since the voltage sensed on the basis of the amount of current of the secondary coils has no big difference from a sensed voltage in a normal state because of the function of maintaining current balance that operates when each lamp performs an abnormal operation, such as an open-circuit or a short-circuit, it is difficult to sense lamp failures.